Percussion drill bit and method of drilling a borehole

ABSTRACT

A percussion drill bit includes a bit body having a central axis and a bit face. A plurality of inserts is disposed on the bit face. A plurality of gauge row inserts is disposed on a periphery of the bit face. At least some one of the plurality of gauge row inserts is enhanced with a super hard material and oriented on the periphery of the bit face at an angle between about 36 degrees and about 40 degrees relative to the central axis of the bit body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This applications claims benefit, under 35 U.S.C. § 119, of U.S. Provisional Application Ser. No. 60/799,782 filed on May 11, 2006 and entitled “Percussion Drill Bit and Method of Drilling a Borehole” in the name of Lance Underwood and Ronald Schmidt, and incorporated herein by reference in its entirety.

BACKGROUND

The disclosure herein generally relates to earth boring bits used to drill a borehole for applications including the recovery of oil, gas or minerals, mining, blast holes, water wells and construction projects. More particularly, the disclosure relates to percussion hammer drill bits. In percussion hammer drilling operations, the bit impacts the earth in a cyclic fashion while simultaneously rotating. In such operations, the mechanism for penetrating the earth is of an impacting nature rather than shearing. A typical percussion drill bit comprises a drill body, means at one end of the drill body for connecting the bit to a percussive unit such as a down hole hammer, and at the other end, a bit face including a plurality of inserts for impacting and fracturing earthen formations.

Inserts are typically disposed on various portions of the bit face. For example, in FIG. 3, inserts are shown disposed on the central portion 19 of the bit face 14 in the proximity of the central axis 13 of the bit 10, and inserts 20, 22 are disposed in numerous circumferential rows on the bit face 14, such as a first row 72, second row 74, third row 76 and gauge row 70. The term “gauge row” as used herein refers to the row 70 extending around or adjacent, the periphery, or edge, 15 of the bit face 14. Gauge row inserts 20 are positioned around the periphery of gauge row 70. The bit face 14 also included one or more fluid flow openings 16 and flow channels 18 for allowing the flow of circulation fluid (not shown) from within the bit 10 to the exterior 44 of the bit 10.

An example of a typical hammer bit connected to a rotatable drill string is described in U.S. Pat. No. 4,932,483, incorporated herein by reference in its entirety. The down hole hammer comprises a top sub and a drill bit separated by a tubular housing incorporating a piston chamber there between. A feed tube is mounted to the top sub and extends concentrically into the piston chamber. A piston is slideably received within the housing and over the feed tube. Fluid porting is provided in the feed tube and the piston to sequentially admit fluid in a first space between the piston and top sub to drive the piston towards the drill bit support and to a second space between the piston and the drill bit support to drive the piston towards the top sub.

Rotary motion is provided to the hammer assembly and drill bit by the attached drill string powered by a rotary table typically mounted on the rig platform. The drill bit is rotated through engagement of a series of splines on the bit and driver sub that allow axial sliding between the components but do not allow significant rotational displacement between the hammer assembly and bit.

The gauge row inserts typically comprise a cemented carbide body having a rear mounting portion embedded in the bit head and a front end protruding from the bit head. A super hard material, such as polycrystalline diamond layer, is provided on the protruding end of the carbide body, the material having an end edge disposed in the vicinity of the maximum diameter of the insert.

Known drill bits that are provided with gauge inserts enhanced with a super hard material often have a disadvantage in that premature failures occur due to fatigue or chipping of the super hard material. A reason for the failure is that the point of contact between the wall of the bore and the gauge insert is close to, or on, the rear edge area of the super hard material coating. The coating is very thin at that area and thus has a comparatively poor resistance to wear. The known drill bits more or less drill the bore diameter with the thinnest part of the gauge insert since their gauge inserts are inclined by about 35 degrees. Other know bits, such as those described in U.S. Pat. No. 5,575,342 to Hedlund, disclose inserts that are inclined by about 41 degrees to about 51 degrees, and preferably about 45 degrees. While angling these inserts with a 41 to 51 degree range increase the distance between the rear edge of the super hard material coating and the borehole, the increased angle results in increased stresses on the gauge row inserts resulting in premature wear and failure.

Different places on the bit head may see different conditions during. A need exists for a drill bit with inserts at different orientations on the bit head to better match the varying conditions or applications of different places on the bit head.

The embodiments of the present disclosure described herein provide opportunities for improvement in percussion bit service life and rate of penetration. These and various other characteristics and advantages will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the disclosure, and by referring to the accompanying drawings.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a percussion drill bit for percussive drilling in a formation is provided that includes a bit body having a central axis and a bit face. A plurality of inserts is disposed on the bit face. A plurality of gauge row inserts is disposed on a periphery of the bit face. At least some one of the plurality of gauge row inserts is enhanced with a super hard material and oriented on the periphery of the bit face at an angle between about 36 degrees and about 40 degrees relative to the central axis of the bit body.

In another aspect of the present disclosure, a method of designing a percussion drill bit including a bit body having a central axis and a bit face is provided. The method includes modeling a gauge row insert comprising a wear pattern, performing finite element analysis (“FEA”) on the modeled gauge row insert, wherein the modeled gauge row insert is oriented at a first angle relative to the central axis of the bit body, repeating the performed FEA with the modeled gauge row insert at a second angle relative to the central axis of the bit body, and selecting an angle for a plurality of gauge row inserts from the performed FEA.

Other aspects and advantages of the disclosure will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiments, reference will now be made to the accompanying drawings, wherein:

FIG. 1 is a cross-section of a percussion hammer drilling assembly;

FIG. 2 is an elevational view of a percussion drill bit;

FIG. 3 shows a front view of a percussion drill bit.

FIG. 4A shows a sectional view of a percussion hammer bit according to the present disclosure.

FIG. 4B shows a sectional view of a gauge insert according to the present disclosure, in relation to a borehole wall;

FIG. 5 shows a table with calculated stresses exerted on a gauge row insert in relation to the inserts orientation according to angle A; and

FIG. 6 is a graphical representation of the data shown in FIG. 5.

FIG. 7 is a finite element analysis of a gauge row insert, illustrating areas of stress on the insert after it has begun to wear.

DETAILED DESCRIPTION

Referring first to FIG. 1, a cross-section of a typical percussion drilling assembly 200 is attached to a drill string 210. Assembly 200 comprises a top sub 220 threadably connected to a case 230, which is threadably connected to a driver sub 240. A bit 10 is slideably engaged with driver sub 240, and a retainer sleeve 250 is disposed between case 230 and bit 10. Top sub 220 further comprises a check valve 225 and a feed tube 235 that extends from check valve 225 to a piston 245 that is slideably engaged with a guide sleeve 255.

During operation, drill string 210 rotates, thereby rotating percussion drilling assembly 200. In addition, piston 245 travels back and forth in an axial direction so that it cyclically impacts bit 10. A series of engaged splines 265 on bit 10 and driver sub 240 allow bit 10 to slide axially relative to driver sub 240 while also allowing driver sub 240 to rotate bit 10. As described previously, this allows the cutting elements or inserts 20, 22 (not shown) of bit 10 to be “indexed” to fresh rock formations during each impact of bit 260, thereby improving the efficiency of the drilling operation.

Referring now to FIG. 2, a percussion bit 10 for earth-boring applications comprises a body 90 with a drill string end 12 (nearest a drill string, not shown) and a bit face 14. A plurality of splines 30 are disposed on body 90 between a threaded portion 40 and a recessed portion 50. Body 90 further comprises a collar 60 near drill string end 12 and a flared portion 70 near bit face 14.

In FIG. 3 there is shown a top view of the bit face 14 of a drill bit 10 according to the present disclosure, the bit being generally symmetrical about its central axis 13. Provided in a bit face 14 of the drill body 90 is a number of inserts. The inserts are made of cemented carbide and secured into the face of the bit. A number of gauge row inserts 20 is positioned at the periphery of the bit 10, the radially outer portions of which define the diameter of the bit and thus the diameter of the bore being drilled.

As shown in FIG. 4A, the gauge row inserts 20 are tilted in such a way, that a longitudinal center line (center axis) 77 of each insert 20 diverges by an angle A from the central axis 13 of the drill bit 10 in a forward direction of the bit. Several gauge row inserts 20 may be embedded in the bit face 14. Each insert 20 comprises a cemented carbide body having a cylindrical grip or mounting portion 71 embedded in the drill body and a front end protruding from the drill body. A super hard material, such as a polycrystalline diamond layer 72 is provided on the front end of the carbide body to define the cutting end of the insert 20. As shown in FIG. 4B, the layer 72 has a rear edge 75 substantially lying in a plane P. The plane P preferably forming an acute angle with the center axis 13, that angle being equal to the above-mentioned angle A. The edge 75 is disposed preferably at or in the vicinity of the maximum diameter of the insert. The central axis 13 of the drill bit 10 and the longitudinal center line 17 of the inserts 20 define the angle A there between.

When calculating stress on a new insert, stresses will generally be linear with respect to center line 17; however, once an insert begins to wear, points of higher stress are observed. To predict these stresses, in one embodiment, a “cat eye” wear pattern is modeled on the insert for the percussion drill bit. After modeling the worn insert, finite element analysis (“FEA”) is performed on the worn insert to determine stresses. The FEA performed by the present inventors on the worn insert revealed that the relationship between angle A and the stress is nonlinear, unlike the linear relationship between stress and angle A for the new insert. Particularly, the point of highest stress will occur along the bottom of the cat eye wear pattern as shown in FIG. 7. FIG. 5 displays the highest calculated stress once wear begins to occur on the inserts depending upon the orientation of inserts 20 in relation to angle A. For example, when angle A is 30 degrees, the stress on insert 20 is calculated to be 9,639 psi. When angle A is 42 degrees, the stress on insert 20 is calculated to be 11,021 psi. When angle A is 38 degrees, stress on insert 20 is calculated to be 8,783 psi. FIG. 6 illustrates the corresponding stress in psi relative to angle A in a graphical manner, illustrating the nonlinear calculated stresses on inserts, once wear has begun.

In a preferred embodiment, the angle A is in the range of at least 36 degrees to about 40 degrees, in order to space the edge 75 by a distance L from the wall of the bore during drilling. More preferably, the angle A is about 37 degrees to 39 degree and most preferably is about 38 degrees. The distance L is at least 0.020 inches, and more preferably greater than 0.025 inches.

The present disclosure further relates to a method of maintaining the diameter of a drill bit during percussive drilling of a bore in a rock material. The method comprises the following steps: providing a drill bit having the geometry described above, connecting the bit to a percussive unit and drilling a bore, while spacing the rear edge of the diamond layers of the gauge inserts from the wall of the bore during drilling so as to maximize the duration of the life of the bit.

The disclosure can be varied freely within the scope of the appended claims. For example the shape of the cutting end of the insert can be semi-spherical or bullet-shaped.

Although the present disclosure has been described in connection with a limited number of embodiments, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the disclosure as defined in the appended claims.

While various preferred embodiments of the present disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments herein are exemplary only, and are not limiting. Many variations and modifications of the methods and apparatuses disclosed herein are possible and within the scope of the disclosure. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. 

1. A percussion drill bit, comprising: a bit body having a central axis; a bit face; a plurality of inserts disposed on the bit face a plurality of gauge row inserts disposed on a periphery of the bit face, wherein at least one of the plurality of gauge row inserts is enhanced with a super hard material and oriented on the periphery of said bit face at an angle between about 36 degrees and about 40 degrees relative to the central axis of the bit body.
 2. The percussion drill bit of claim 1, wherein at least one of the plurality of gauge row inserts is bullet-shaped.
 3. The percussion drill bit of claim 1, wherein at least one of the plurality of gauge row inserts is semi-spherical.
 4. A method of designing a percussion drill bit comprising a bit body having a central axis and a bit face, the method comprising: modeling a gauge row insert comprising a wear pattern; performing finite element analysis (“FEA”) on the modeled gauge row insert, wherein the modeled gauge row insert is oriented at a first angle relative to the central axis of the bit body; repeating the performed FEA with the modeled gauge row insert at a second angle relative to the central axis of the bit body; selecting an angle for a plurality of gauge row inserts from the performed FEA.
 5. The method of claim 4, wherein the wear pattern is a cat eye pattern.
 6. The method of claim 4, wherein the first angle and the second angle are between about 36 degrees and about 40 degrees relative to the central axis of the bit body.
 7. A percussion drill bit designed using the method of claim
 4. 